Tuned radio frequency amplifier



April 22, 1930. R s, OHL 1,755,266

TUNED RADIO FREQUENCY AMPLIFIER Filed Dec. 51, 1924 INVENTOR K. (51 Oh ATTQRNEY missnnn; s. oHI", Oahu-Yum, N. Y., AssiGN-onf'ronivinnionmrnnnrnonnignn TELEGRAZBH CQMPANY, Acon-roRArIoN oF'nEW 03K 1 Tj NnnfRA OJEREQUEN Y' AMPLIFIER I "a pl cationfiiea ne embe 31;;1924.=- sunrise-"259,096;

L This invention latesa o radio: fr quen y amplifiers and'particularly to meansfor preventing the sett ng up of oscilla ons n an amp ifier of that type, Wh h sdll-a iQns are of: aafuequency 'fi'eri-ng ;from that forwhich thean plifier is; ned:;--, l 3 I lQne; of; the difiicultie experiencedjin; the

amplificat on ofhighrfnequencies a i e from the tendency vof theiamplifiel nto oscillate; at

freduenciesiwhicl are parasit c to he treq-u 'icya y hichvt e: amplifie is intended to operate; The e osci lations are set. up. by the: capacitybetween ,tihet grid and} the plate ifiz zhfl l bfi and by; theinductance of' the-com duct to mjngpart-of; theinputand out-f put-cite t; of the tube, I which capacity; and

' indnctancebeeome; importantwhem the frequeney winnolved; is iof aeh-igh; order-: ;of.1pe,- riodicitya iliheseioscillations? block a the detector and thus,- pcnevent the detection} '0 frd iredtsignalsa means for preventing a feeding back from the output tothe input circuitrofa highlffrecqneney ampjlifieri'of freqnencies that are para.-

' sitic to the said high frequency; thereby sup;-

pressing any tendency on the part of the amplifier to oscillate at the parasitic frequency.

Other objects of this invention will be apparent from the following description when' read in connection with the attached drawing showing schematically a form of embodiment of thelnvention. i v p I In thev drawing the antennal is connected with the primary winding 2 of afcoupling transformer, of which the secondary windh1g3 is connected with the'input circuit of the vacuum tubeamplifier l. One terminal 7 of winding 3 is connected with the grid 5. The midpoint of 'the'same winding is connected with the unipotential cathode 9. The other terminal of winding 3 is connected through the condenser 6 withthe plate 7 A variable condenser 8 is connected across the terminals of Winding?) .to time the input circuit of the amplifier to the high frequency at which the amplifier is intended to operate The nnipotentialv cathode 9 is rendered active by means of a filament 10, which is connected through the windings 11 -12 of a The object-f this; to: proizide.

grounded. The secondary winding :16 of the transformer is connected. with a Evacuumttube.idetectorill I @116: of the terminals of, the winding 16,-is connected: with 'theig'riid 22: of the deteotor and the other terminalis connected through the condenser-24 with the plate-23; 7 Theinidpoint of winding 16l$0011- nected With-the cathode 28 the connection includingthe Chatter-y 26. The cathode, 28-is rendered. active by a1filament29; whicltis' energized by the sounce-1 -3'. The cathodes-10f eachjof the tubes tand l Z aregrounded at point, 20. 'lhe"p1ate:23 of tube: 1? is; connect.- ed with the source/'18v us plate. potential the connection including a, signal indicating de vi ep ese ym o cal y a t lephone receiver 27. The midpoint of the winding ll is-connected with the negativepol'e; of the source l9 of direct-cunrent potential}, which, for example, may be of thegorder ofmagni} tude, of [from 12 to 222 volts, which; potential primary: winding lt of transformer 15; with the 'positi-vepole of'aisourcel 8of direct current; potential; whichhas itsnegative. pole seen thflEtTthQ,Wllldlngld: is also 'connected to groundthroughthe battery-1:8, so-that the winding 14: andzthelcondenser 21, are in; pairiallel The I mannerin; which this: circuit-j operates to amplify the. high frequencies I uponi-zwhich is as; fO11QWs High frequencies; initendedfto be received; will be: 'impreetsediby: theantenna onant tothe frequency inte-ndedto. be; amplil-hed Thisfrequency wi-lhbeifmpressfled upon parasitic frequencies.

in the space current between the plate 7 and the cathode 9, which space current is derived from the source 18 and flows through the winding 14 of the transformer 15. The high frequency will thus be amplified and impressed upon the resonant input circuit 1625 of the detector 17. 'By the proper adjustment of the C battery 26, the signal will be detected and will be manifested by the signal indicating device 27 If, however, there are present certain parasitic frequencies which, by virtue of the capacity between the grid 5 and the plate 7 and also by virtue of the inductance between the conductorsof the magnitude of the inductance 14. 7 Briefly stated, if the inductive reactance of the windin 14 is less than the capacitative reactance of the condenser 21, for the high frequency intended to be amplified and detected, the input impedance of the transformer-15 will be increased, which condition is,-of course, desirable for such amplificationand detection. However, if the inductive reactance of the Winding 14 is appreciably greater, than the capacit-ative reactance of the condenser 21 for the parasitic frequencies, the impedance of these elements combined becomes less than the impedance due to the inductive reactance alone, and thus no oscillations can take place at-frequencies considerably below the said high frequencies for which the amplifier is intended to function, viz.', at the December, 1924.

Briefly stated, the r 7 1. In a high frequency signaling system, the combination with an amplifier having'a vacuum tube of an input circuitand an output circuit, a detector circuit, a transformer having its primary winding connected with the said amplifier. output circuit and its secondary winding connected with the detector circuit, and a condenser connected in parallel with the said primary winding,,the mag:

nitude of the capacitance and inductance of circuit, a condenser; connected between the said input circuit and output circuit to apply to the input circuit oscillations equal in magnitude and opposite in phase to the oscillations fed back by the inter-electrode capacity of the tube, and a condenser connected in parallel with the said primary winding, the magnitudes of the capacitance and inductance of the said latter condenser and the said primary pedance of the combination is high'for frequencies to be amplified and low forparasitic frequencies whereby oscillation of the amplifier at the said parasitic frequencies is prevented. V V y In testimony whereof, I have signed my name to this specification this 30th day of RUSSELL s. OHL. V

magnitude of the capacity of the condenser 21 is such as to readily pass the parasitic :tre-

quencies and to oppose the passage of the high frequency intended to be amplified. Ittherefore shunts the parasitic frequencies and prevents any tendency of the circuit to oscillate at those frequencies. 7

The invention has been disclosed in a balanced type of input circuit, which circuit is characterized by the condensers 6 and 24 connected between' the input winding and-the plate of the tubes 4 and 17 respectively; This type of circuit has'been chosen to illustrate the invention because it represents a desirable form of circuit for the reception of high frequency signals. It is not to be understood,

pable of embodiment in other and difierent What is claimed is:

however, that the invention is limited to such V a circuit,'because, to the contrary, it is cawinding, respectively, being such that the im- 

